Which of the following statement is not true about the hexagonal close packing ?

(a) The coordination number is 12

(b) It has 74% packing efficiency

(c) Tetrahedral voids of the second layer are covered by the spheres of the third layer

(d) In this arrangement spheres of the fourth layer are exactly aligned with those of the first layer

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Solution

(d) Hexagonal close packing can be arranged by two layers

A and B one over another which can be diagrammatically represented as

Here, we can see easily that 1 st layer and 4th layer are not exactly aligned.

Thus, statement (d) is not correct while other statements (a), (b) and (c) are true.

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Similar questions

Which of the following is not true about the voids formed in 3 dimensional hexagonal close packed structure ?

(a) A tetrehedral void is formed when a sphere of the second layer is present above triangular void in the first layer

(b) All the triangular voids are not covered by the spheres of the second layer

(c) Tetrahedral voids are formed when the triangular voids in the second layer lie above the triangular voids in the first layer and the triangulare shapes of these voids do not overlap

(d) Octahedral voids are formed when the triagular voids in th second layer exactly overlap with similar voids in the first layer

Q. Match the types of packing given in column I with the items given in column II.

	Column I		Column II
(i)	Square close packing in two dimension	(p)	Triangular voids
(ii)	Hexagonal close packing in two dimensions	(q)	Pattern of spheres is repeated in every fourth layer
(iii)	Hexagonal close packing in three dimension	(r)	Coordination number=4
(iv)	Cubic close packing in three dimension	(s)	Pattern of spheres is repeated in alternate layers

Q. Stacking of a second layer of sphere over the first layer of 2-D hexagonal close packing will result in formation of:

Q. In hexagonal systems of crystals, a frequently encountered arrangement of atoms is described as a hexagonal prism. Here, the top and bottom of the cell are regular hexagons and three atoms are sandwiched in between them. A space-filling model of this structure, called hexagonal close-packed (HCP), is constituted of a sphere on a flat surface surrounded in the same plane by six identical spheres as closely as possible. Three spheres are then placed over the first layer so that they touch each other and represent the second layer. Each one of these three spheres touches three spheres of the bottom layer. Finally, the second layer is covered with third layer that is identical to the bottom layer in relative position. Assume radius of every sphere to be 'r'.

The empty space in this HCP unit cell is?

Q. In hexagonal system of crystals, a frequently encountered arrangement of atoms is described as a hexagonal prism. Here, the top and bottom of the cell arc regular hexagons and three atoms are sandwiched between them. A space-filling model of this structure, called hexagonal close packed (hcp), is constituted of a sphere on a flat surface surrounded in the same plane by six identical spheres as closely as possible. Three spheres are then placed over the first layer so that they touch each other and represent the second layer. Each one of these three spheres touches three spheres of the bottom layer. Finally, the second layer is covered with a third layer that is identical to the bottom layer in relative position. Assume radius of every sphere to be 'r'.

The empty space in this hcp unit cell is:

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(d) Hexagonal close packing can be arranged by two layers A and B one over another which can be diagrammatically represented as Here, we can see easily that 1 st layer and 4th layer are not exactly aligned. Thus, statement (d) is not correct while other statements (a), (b) and (c) are true.

(d) Hexagonal close packing can be arranged by two layers

A and B one over another which can be diagrammatically represented as

Here, we can see easily that 1 st layer and 4th layer are not exactly aligned.

Thus, statement (d) is not correct while other statements (a), (b) and (c) are true.